American manufacturer use their own peculiar brand of imperial measurements for pretty much everything. volumes pressures torques etc etc. When you've been flying for a bit the conversions become second nature and its not really a problem. If you want metric, fly european. Even then the aviation industry is littered with inconsistancies. ATC depends where in the world you are. When I did my JAR exams they were littered with inconsistancies. You gotta learn to live with it.